Where did the world’s first footprint, which may have started out as a small step but holds great significance as a huge leap for living creatures, come from?
A research team including Korean researchers Chung Hee-kyung and Baek Myung-in at the NYU School of Medicine published a paper on the origin of the unique motor nerve that created the walking movements of humans and four legged animals such as mice and frogs. The paper was published on Cell, an international journal in life science on Wednesday (local time). According to the research, the animal that left behind the world’s first footprint is thought to have been the ancestor of the skate that lived 420 million years ago in the Paleozoic era.
The research team focused on the skate’s movements in seawater. Skates are flat, and move underwater by alternately moving a pair of small fins on the left and right sides of their bodies. Its movements are quite similar to a human’s walk. In the process, the front and back muscles of the fins contract and relax alternately, which is also quite similar to how the human’s arms and legs move.
The team also showed how the motor nerve of the stake was different from other fish. For most fish, the central nerve system, which consists of the brain and spinal cord, is in a single straight line, but the skate has an expanded motor nerve that branches out from the back fin. Decoding the RNA of the skate’s motor nerve revealed the gene was associated with the nerve. Thus the team discovered that the skate’s gene is the same gene that controls the leg movements of four legged animals today. In other words, the skate and four-legged animals have inherited walking movements from the same ancestors.
Based on this discovery, the research team assumed that the “walking motion” had originated, from the chondrichthyes, which lived some 420 million years ago. The finding suggests that it was several hundred years earlier to what previous fossil-based research had revealed. “Mammals and skates walk in the same way in both neurological and genetic ways. The skate may become an animal model for research on walking,” said Jeremy Dayson, head of the team and professor at the NYU medical school.